The present invention relates to a wire stitching or stapling machine of the type which severs and forms staples from a continuous wire and drives the staples into an associated workpiece. In particular, the invention relates to a stitching head for such a machine.
The present invention is an improvement of the wire loop stitching machine head disclosed in the copending application Ser. No. 420,046 of Alfred J. Gruen, filed Sept. 20, 1982, and assigned to the assignee of the present invention. That stitching machine head is, in turn, an improvement of the wire stitching machine sold by Interlake, Inc. under the trademark "CHAMPION STITCHER". This prior stitching machine includes a stitching head having a wire feed mechanism for feeding a predetermined length of wire from a continuous wire supply to a wire holder, where the length of wire is severed from the supply, and a staple-forming and driving mechanism which forms the severed length of wire into a staple and drives it into an associated workpiece. The mechanism undergoes a cyclical reciprocating movement comprising a drive stroke and a return stroke. During each drive stroke the feed means is feeding a predetermined length of wire to the wire holder, while the staple-forming and driving means is forming and driving the length of wire which had been fed during the preceding drive stroke. Both mechanisms then retract simultaneously, and at the end of each cycle there is left in the wire holder a severed length of wire ready to be formed and driven during the next drive stroke.
A bender in the stitching head operates to form a standard staple which is substantially in the shape of an inverted-U, having a pair of parallel leg portions interconnected by a straight bight portion disposed substantially perpendicular to the leg portions. A supporter then moves, under the urging of bias means and the guidance of a guide plate from a retracted position to a supporting position between the legs of the staple. The supporter has a rounded projection thereon which cooperates with the staple forming and driving means to form the bight portion of the staple or a part thereof into a "loop". Continued movement of the staple forming and driving means then drives the formed staple through an associated workpiece, the legs being folded over by a clincher to complete the stapling or stitching operation. During this driving of the formed staple, the staple forming and driving means cams past the supporter and pushes it back out of the way toward its retracted position. During the return stroke of the staple forming and driving means, the supporter is guided the rest of the way to its retracted position by the guide plate.
It has been found that in practice, during the formation of the loop portion of the staple, the pressure of the staple forming and driving means against the supporter projection has tended to push the supporter back slightly toward its retracted position against the urging of the bias means, thereby resulting in an improper or incompletely formed loop portion, or misalignment of the formed staple. Furthermore, after formation of the loop portion of the staple, the supporter would sometimes hang up and be delayed in movement toward its retracted position by the staple forming and driving means. This would cause undesirable wear on the loop-forming projection of the staple supporter, and might even cause jamming of the machine.